The present invention relates to gas discharge devices, such as those used to create luminous displays or signs; and particularly to the power supply for exciting the gas discharge device.
Luminous displays are constructed by infusing a gas, such as neon or argon, into a hermetically sealed transparent structure, such as a tube or a sandwich of plates. When a high alternating excitation voltage directly or indirectly is applied to the gas, the gas ionizes causing it to glow.
The conventional power supply for applying the excitation voltage to the gas discharge device merely comprised a high voltage transformer which stepped the supply line voltage (120 volts at 60 Hertz or 240 volts at 50 Hertz) up to the high excitation voltage. An alternative type of high voltage power supply is commonly referred to as a resonant converter and is described in U.S. Pat. No. 4,613,934. In this device, the primary winding of the transformer was connected to a resonant circuit which applied pulses of the rectified supply line voltage to the primary winding. Because of the resonant nature of the supply circuit, the peak voltage applied to the primary winding was several times the supply line voltage and the frequency of the primary voltage is several hundred times the supply line frequency. This enabled the number of windings of the primary to be reduced, and the transformer core made lighter.
Neither of these previous power supplies offered any protection to the user from electrical shock which occurred when the user came into contact with a high voltage conductor and a grounded component. Ground fault protection has been employed in various types of electrical devices by connecting a ground fault circuit interrupter (GFCI) to the electrical supply lines to the device. However, merely connecting the GFCI to the 120 volt or 250 volt supply line for a neon sign power supply does not offer protection from a shock at the high voltage side of the transformer.